PMID-35985340 – Retatrutide Discovery to Clinical Proof of Concept
Coskun T, Urva S, Roell WC, et al. LY3437943, a novel triple GIP, GLP-1, and glucagon receptor agonist for glycemic control and weight loss: From discovery to clinical proof of concept. Cell Metabolism. 2022;34(9):1234-1247.e9.
Quick Reference
| Property | Value |
|---|---|
| PMID | 35985340 |
| DOI | 10.1016/j.cmet.2022.07.013 |
| Year | 2022 |
| Journal | Cell Metabolism |
| Study Type | Preclinical + Phase 1 RCT (first-in-human) |
| Evidence Level | II |
| Sample | Preclinical: diet-induced obese (DIO) mice; Phase 1: n=72 healthy volunteers and adults with T2D |
| Peptide(s) Studied | Retatrutide |
Key Findings
- Retatrutide (LY3437943) was rationally designed as a single molecule with balanced agonism at GIP, GLP-1, and glucagon receptors, representing the first triple incretin agonist to enter clinical development
- In DIO mouse models, retatrutide reduced body weight by >20%, superior to dual GIP/GLP-1 and GLP-1/glucagon agonists, driven by both decreased food intake and increased energy expenditure
- The glucagon receptor component contributed to increased energy expenditure and hepatic lipid oxidation without causing hyperglycemia, as GLP-1 and GIP activity provided glycemic counterbalance
- Phase 1 single ascending dose study in humans demonstrated persistent, dose-dependent weight loss even after a single subcutaneous injection, with effects lasting several weeks
- In Phase 1 multiple ascending dose cohorts (12 weeks), participants with T2D showed clinically meaningful HbA1c and body weight reductions
- Preclinical mechanistic studies confirmed that the triple agonist engaged distinct and complementary metabolic pathways: GIP for insulin sensitization, GLP-1 for appetite suppression and glucose-dependent insulin secretion, and glucagon for thermogenesis and lipid metabolism
Study Design
Two-part study: (1) Preclinical discovery and characterization in cell-based receptor activation assays, pharmacokinetic studies, and efficacy studies in DIO mice comparing triple agonist to mono- and dual-agonist controls; (2) Phase 1 first-in-human randomised, double-blind, placebo-controlled single ascending dose (SAD) and multiple ascending dose (MAD) trial in healthy participants and adults with T2D. SAD: single subcutaneous doses with 12-week follow-up. MAD: weekly subcutaneous dosing for 12 weeks.
Limitations
- Preclinical mouse data may not fully translate to human metabolic physiology, particularly regarding glucagon-mediated energy expenditure
- Phase 1 trial had small sample sizes per cohort, limiting statistical power for safety and efficacy conclusions
- The Phase 1 population was relatively healthy; applicability to patients with advanced T2D, cardiovascular disease, or significant comorbidities is unknown
- Long-term safety of chronic glucagon receptor agonism in humans remains to be established
- Energy expenditure measurements were not directly performed in the human Phase 1 cohorts
Clinical Relevance
This foundational paper describes the rational design and initial clinical validation of retatrutide as a first-in-class triple incretin agonist. The key mechanistic insight—that adding glucagon agonism to GIP/GLP-1 activity produces additive weight loss through increased energy expenditure without hyperglycemia—provides the scientific basis for the entire retatrutide clinical program. The persistent weight loss observed after even single doses in Phase 1 foreshadowed the exceptional efficacy results seen in subsequent Phase 2 trials. This paper is essential reading for understanding the pharmacological rationale behind triple agonist therapy and its potential advantages over dual agonists like tirzepatide.
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#research #RCT #evidence-level-II #retatrutide #metabolic